This application claims the priority of German Patent Application No. 197 35 012.7, filed Aug. 13, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for manufacturing a cast cylinder head for an internal combustion engine, as well as a cast cylinder head of an internal combustion engine.
According to known practice, cylinder heads are manufactured almost exclusively by casting. Usually, casting molds are used whose outer margins are formed by casting dies, made of steel for example. To form inlet and outlet channels as well as a space for the cooling water in the cylinder head (i.e., the so-called water chamber), sand cores made of casting sand are suspended in the casting dies.
Following the casting process, the sand cores are initially mechanically comminuted and then usually blown out of the hollow spaces thus formed in the cylinder head, using compressed air. As a result of various parameters required in casting technology, such as parting planes for example, drafts, or casting wall thicknesses, it is not possible to design the water chamber freely. As a result, optimum cooling of the combustion chambers located in the lower area of the cylinder head by the cooling water cannot be achieved.
The poor cooling of the combustion chambers is also caused by the fact that as a result of the cooling water being added from a crankcase located beneath the cylinder head, the cooling water already has a powerful momentum toward the upper area of the water chamber. In addition, accumulations of castings should always be avoided in cast parts, so that the water chamber must be designed very much larger than necessary in the cylinder head.
U.S. Pat. No. 4,690,104 describes a cylinder head manufactured by casting for an internal combustion engine that has an opening in the upper area into which a cup-shaped part is screwed. The cooling water stream is intended to be conducted through this part toward the combustion chambers, with the opening simultaneously being used to remove the casting sand.
However, the relatively cumbersome screwing in of the cup-shaped part is disadvantageous, with additional sealing devices being required in order to seal off the water chamber of the cylinder head reliably. In addition, in this cylinder head, considerable mechanical effort is required to make a very large threaded bore for the cup-shaped part.
A cylinder head is disclosed in British Patent No. 563,789 that is provided with a cover plate on its upper side that is held in place by bolts. On the side of the cover plate that faces the interior of the cylinder head, a distributor plate is fastened by additional bolts, with this distributor plate being intended to ensure that the cooling water flowing through the cylinder head is located for the most part in the vicinity of the combustion chambers.
The goal of the present invention is to provide a method for manufacturing a cylinder head that makes it possible by very simple means for the coolant contained in a water chamber of the cylinder head to cool very well, especially to cool the combustion chambers located in the lower area of the cylinder head.
According to the present invention, a displacement body, which remains in the water chamber of the cylinder head, produces an improved distribution of the flow of coolant in the cylinder head, especially a concentration of the coolant stream at the tops of the combustion chambers located in the lower part of the cylinder head.
This improved cooling advantageously results in a reduction in the power of a water pump, lower fuel consumption, and a higher tolerance for knocking.
Another advantage of the displacement body located in the water chamber is that the quantity of coolant in the internal combustion engine can be reduced considerably as a result. This reduction results in a shorter warm-up phase for the engine so that pollutant emissions and frictional work are reduced, while driving comfort, heating response, and rate of defrosting and defogging of the windows are increased.
The displacement body according to the present invention offers another positive aspect by virtue of the fact that it can contribute to stiffening the cylinder head.
Moreover, a large quantity of casting sand can be saved as a result of the displacement body being located in the sand core.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the present invention when considered in conjunction with the accompanying drawings.